The present invention relates to adhesion promoters that improve adhesion between film-forming coatings and adhesives and polyolefinic substrates. The adhesion promoters are prepared by controlled radical polymerization using a halogenated polyolefin as a macroinitiator.
Polyolefins, such as polypropylene and polyethylene are used in a wide variety of molding applications including, for example, in preparation of molded parts for use in the automotive, industrial and appliance markets. The preparation of such molded articles generally includes the steps of molding an article from the polyolefin resin and applying to the molded article one or more film-forming coating layers to protect and/or color the article and/or an adhesive to attach the molded article to another article.
One difficulty with use of poyolefinic substrates is that typical film-forming coatings and adhesives do not adhere well to the substrate. In the case of a film-forming coating applied to the substrate, the layer delaminates. In the case of adhesives, adhesive failure is commonplace.
A solution to the failure of coatings and adhesives to adhere to the polyolefinic substrate is to include a layer of a film-forming composition including a chlorinated polyolefin (CPO) between the substrate and the film-forming coating or adhesive. This adds a processing step and, since chlorinated polyolefins are relatively expensive, adding to the cost of using polyolefins to produce molded parts.
U.S. Pat. No. 5,955,545 discloses use of CPO-acrylic graft copolymers as adhesion promoters that assertedly improve adhesion of subsequent coating layers and/or adhesives to polyolefins. However, these graft copolymer adhesion promoters are prepared by standard free radical polymerization methods and suffer from high polydispersity and the presence of non-graft polymer chains and acrylic copolymers and homopolymers in the resin composition as a result of the random nature of standard radical polymerization processes. The high polydispersity and additional non-graft chains present in the same mixture as the graft polymer results in incomplete or inefficient adhesion promotion and interference with the curing dynamics of the resin. Further, these compositions are unstable, readily falling out of solution, especially when incorporated in a film-forming composition, and they absorb and scatter light, giving a hazy appearance. Thus, they are unsuitable for many coating applications.
It is, therefore, desirable to have well defined adhesion promoting material that includes polyolefinic segments or portions that interact strongly with polyolefinic substrates as well as portions or non-polyolefinic segments that interact well with film-forming resins, crosslinkers and/or curing agents and solvents that are present in a typical coating composition. It is also desirable that the adhesion promoter be of a more defined architecture than is typically found in graft copolymers formed by a free radical process. The defined architecture will allow for design of copolymers that interact with other components of the coating composition in a consistent manner with less contamination with undesirable polymer species that typically result from free radical grafting to CPOs. The low polydispersity of the material, combined with the substantial absence of undesirable polymer species would yield a clear, stable coating additive or coating composition that would adhere well to polyolefinic substrates.
A wide variety of radically polymerizable monomers, such as methacrylate and acrylate monomers, are commercially available and can provide a wide range of properties including, for example, hydrophilic and hydrophobic properties, the ability to interact with crosslinkers, or to self crosslink.
U.S. Pat. Nos. 5,807,937; 5,789,487; and 5,763,548 and International Patent Publication Nos. WO 98/40415; WO 98/01480; WO 97/18247; and WO 96/30421 describe a radical polymerization process referred to as atom transfer radical polymerization (ATRP). The ATRP process is described as being a living radical polymerization that results in the formation of (co)polymers having predictable molecular weight and molecular weight distribution. The ATRP process is also described as providing highly uniform products having controlled structure (i.e., controllable topology, composition, etc.). The ""937 and ""548 patents also describe (co)polymers prepared by ATRP, which are useful in a wide variety of applications including, for example, dispersants and surfactants.
U.S. Pat. Nos. 5,478,886; 5,272,201; 5,221,334; 5,219,945; 5,085,698; 4,812,517; and 4,755,563 describe ABC, AB and BAB block copolymers and pigmented ink compositions containing such block copolymers. The block copolymers of the ""886, ""201, ""334, ""945, ""698, ""517 and ""563 patents are described as being prepared by living or stepwise polymerization processes, such as anionic or group transfer polymerization.
A number of initiators and macroinitiators are known to support ATRP polymerization. These initiators are described, for example, in U.S. Pat. Nos. 5,807,937 and 5,986,015. U.S. Pat. No. 5,807,937 discloses a number of initiators, including a macroinitiator, where halide groups attached to an activated benzylic carbon serve as the initiating site. The ""937 patent discloses that benzyl halides can be efficient initiators for ATRP in monomeric form as well as in a polymer.
WO 9840415 Al discloses ATRP macroinitiators having an activated halogen, which have been prepared by chlorosulfonation of polyethylene. The chlorosulfonyl group is known to be a good ATRP initiator in monomeric form.
Paik et al. (xe2x80x9cSynthesis and Characterization of Graft Copolymers of Poly (vinyl chloride) with Styrene and (Meth) acrylates by Atom Transfer Polymerizationxe2x80x9d, Macromol. Rapid Commun., 19, 47-52(1998)) disclose that polyvinyl chloride is incapable of serving as an initiator in an ATRP process. Paik further discloses that ATRP can be initiated by the activated chlorine in a chloroacetate group attached to a PVC backbone. Paik also discloses that the secondary chlorines on the PVC backbone do not initiate ATRP. Collectively, the prior art indicates that effective ATRP macroinitiators should contain activated halogens.
In accordance with the present invention, an alkenyl (co)polymer is provided that is prepared by polymerizing alkenyl monomers in the presence of an initiator or macroinitiator (collectively xe2x80x9can initiatorxe2x80x9d) having halide groups attached to tertiary carbons under atom transfer radical polymerization conditions. An example of such an initiator is, without limitation, a halogenated polyolefin such as a chlorinated or brominated polypropylene, polybutylene or branched polyethylene. This polymer finds use in a variety of applications, such as, without limitation, in compositions for coating, molding and extruding. A typical use for the copolymer is as an additive to a film-forming resin composition for coating a polyolefinic substrate. The additive both promotes interlayer adhesion between the coating composition layer and the polyolefinic substrate and can be crosslinked into the film-forming resin.
A curable film-forming composition including the alkenyl-halogenated polyolefin copolymer is also provided. The halogen content of the halogenated polyolefin embodiment is typically either chlorine or bromine. The number of halide groups in the initiator can vary, but typically falls between about 15% to 45% by weight of the initiator, as is commonly found in commercially available halogenated polyolefins.
A method of coating a polyolefinic substrate also is provided that includes applying to the polyolefinic substrate a film-forming composition comprising the above-described vinyl-halogenated polyolefin copolymer. A coated article prepared according to the method is also described.
Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc, used in the specification and claims are to be understood as modified in all instances by the term xe2x80x9caboutxe2x80x9d. As used herein, the term xe2x80x9cpolymerxe2x80x9d, and the like, is intended to include both polymers and oligomers unless stated otherwise. The term xe2x80x9ccopolymerxe2x80x9d is intended to include both random or block copolymers unless specified otherwise.
As described above, the present invention is a polymeric composition prepared by an ATRP process. The process utilizes a novel ATRP initiator that expands the type of copolymers that can be prepared by the ATRP process and the uses therefor. The initiator is a halogenated polyolefin, resulting in the production of a graft copolymer useful as an additive in a coating composition for polyolefinic substrates, among other uses. By the term xe2x80x9cpolyolefinic substratexe2x80x9d it is meant as a substrate having, on at least a portion of its surface, a polyolefinic composition.
The copolymer of the present invention is prepared by controlled radical polymerization. As used herein and in the claims, the term xe2x80x9ccontrolled radical polymerizationxe2x80x9d, and related terms, e.g., xe2x80x9cliving radical polymerizationxe2x80x9d, refer to those methods of radical polymerization that provide control over the molecular weight, polymer chain architecture and polydispersity of the resulting polymer. A controlled or living radical polymerization is also described as a chain-growth polymerization that propagates with essentially no chain transfer and essentially no chain termination. The number of living polymer chains formed during a controlled radical polymerization is often nearly equal to the number of initiators present at the beginning of the reaction. Each living polymer chain typically contains a residue of the initiator at what is commonly referred to as its tail and a residue of the radically transferable group at what is commonly referred to as its head.
In an embodiment of the present invention, the copolymer is prepared by atom transfer radical polymerization (ATRP). The typical ATRP process can be described generally as including the steps of polymerizing one or more radically polymerizable monomers in the presence of an initiation system; forming a polymer; and isolating the formed polymer. In the present invention, the initiation system comprises a halogenated polyolefinic initiator; a transition metal compound, i.e., a catalyst, which participates in a reversible redox cycle with the initiator; and a ligand, which coordinates with the transition metal compound. The ATRP process is described in further detail in International Patent Publication WO 98/40415 and U.S. Pat. Nos. 5,807,937; 5,763,548 and 5,789,487.
In the present invention, ATRP is performed using a polymer which has not been modified to introduce a known activated halogen group or has it been modified as the result of copolymerization of a monomer containing a known activated halogen group. Thus, in the present invention, an unmodified halogen containing polymer is the site for ATRP initiation. Post polymerization modification or inclusion of a special ATRP initiating monomer are not required. This avoids additional process steps in the first case and avoids making a special copolymer in the second.
There are a number of potential explanations as to the exact chemical reason for ATRP functioning well in an unmodified halogen containing polymer, without the presence of the prior art activated halogens. Without wishing to be bound to any single theory, it is believed that the inductive effect of other halogens on the main polymer chain in proximity to the initiating halogen is responsible for its ability to initiate ATRP. Given the free radical nature of ATRP, it is believed that the tertiary halogens on the polymer are the most prone to act as ATRP initiation sites.
Catalysts that may be used in the ATRP preparation of the copolymer of the present invention include any transition metal compound that can participate in a redox cycle with the initiator and the growing polymer chain. It is preferred that the transition metal compound not form direct carbon-metal bonds with the polymer chain. Transition metal catalysts useful in the present invention may be represented by the following general formula (I),
TMn+Xnxe2x80x83xe2x80x83(I) 
wherein TM is the transition metal, n is the formal charge on the transition metal having a value of from 0 to 7, and X is a counterion or a covalently bonded component. Examples of the transition metal (TM) include, but are not limited to, copper, iron, gold, silver, mercury, palladium, platinum, cobalt, manganese, ruthenium, molybdenum, niobium and zinc. Examples of X include, but are not limited to, halide, hydroxy, oxygen, C1-C6-alkoxy, cyano, cyanato, thiocyanato and azido. A preferred transition metal is Cu(I) and X is preferably halide, e.g., chloride. Accordingly, a preferred class of transition metal catalysts are the copper halides, e.g., Cu(I)Cl. It is also preferred that the transition metal catalyst contain a small amount, e.g., one mole percent, of a redox conjugate, for example, Cu(II)Cl2 when Cu(I)Cl is used. Additional catalysts useful in preparing the polymer are described in U.S. Pat. No. 5,807,937 at column 18, lines 29 through 56. Redox conjugates are described in further detail in U.S. Pat. No. 5,807,937 at column 11, line 1 through column 13, line 38.
Ligands that may be used in the ATRP preparation of the copolymer include, but are not limited to, compounds having one or more carbon, nitrogen, oxygen, phosphorus and/or sulfur atoms, which can coordinate to the transition metal catalyst compound, e.g., through sigma and/or pi bonds. Classes of useful ligands include, but are not limited to, unsubstituted and substituted pyridines and bipyridines; porphyrins; cryptands; crown ethers, e.g., 18-crown-6; polyamines, e.g., ethylenediamine; glycols, e.g., alkylene glycols, such as ethylene glycol and carbon monoxide. As used herein and in the claims, the term xe2x80x9c(meth)acrylatexe2x80x9dand similar terms refer to acrylates, methacrylates, and mixtures of acrylates and methacrylates. A preferred class of ligands are the substituted bipyridines, e.g., 4,4xe2x80x2-dialkyl-bipyridyls. Additional ligands that may be used in preparing the polymer are described in U.S. Pat. No. 5,807,937 at column 18, line 57 through column 21, line 43.
The present invention utilizes novel macroinitiators that are typically halogenated polyolefins. The initiator includes one or more ATRP initiation sites that is a halide group attached to a tertiary carbon (hereinafter xe2x80x9ctertiary halidexe2x80x9d). A halide group that is capable of serving as an ATRP initiation site, whether or not a tertiary, secondary or primary halide, or otherwise, is hereinafter referred to as a xe2x80x9cdormant halidexe2x80x9d, as opposed to a halide that is not capable of serving efficiently as a site of ATRP initiation.
Suitable macroinitiators include, without limitation, halogenated polyolefins such as polypropylene and polybutylene. The halide group is typically chlorine and/or bromine. The macroinitiator also can be a branched polyethylene containing a suitable number of tertiary halides.
As used herein and in the claims, by xe2x80x9colefinxe2x80x9d and like terms it is meant unsaturated aliphatic hydrocarbons having one or more double bonds, such as obtained by cracking petroleum fractions. Specific examples of olefins include, but are not limited to, propylene, 1-butene, 1,3-butadiene, isobutylene and diisobutylene. A xe2x80x9cpolyolefinxe2x80x9d is a polymer formed from olefins. Common examples are polypropylene and polybutylene and include the class of thermoplastic polyolefins (TPOs). The polyolefin may be homopolymeric or copolymeric. A variety of homopolymeric halogenated polyolefins are available from Eastman Chemical Company, among others. A halogenated polyolefin is a halogen-substituted polyolefin, and is typically chlorinated or brominated.
There is no literal limit as to the density of halides on the polyolefin backbone of the initiator. However, the halogenated polyolefin typically is a chlorinated or brominated polyolefin having 15% to 45% by weight halide groups, with at least about 80% of the halides being attached to tertiary carbons and, therefore, being dormant halides. Halogenated polyolefins having 15% to 45% by weight halide groups represent most commercially available halogenated polyolefins. However, when halogenated polyolefins having 15% to 45% by weight, halide groups are used as ATRP initiators, the resultant ATRP-produced copolymers are preferred as adhesion promoters for coating compositions used to coat polyolefinic substrates. Having a higher density of halide groups on the polyolefinic backbone of the initiator typically results in insufficient adhesion of copolymer-containing coating to the polyolefinic substrate. Too little halogenation of the polyolefinic backbone of the macroinitiator may result in poor compatibility of the copolymer with the coating composition in which it is dispersed and lack of other desirable functionality in the copolymer, such as sufficient crosslinking density. The most preferred halide group density on the polyolefin initiator will depend upon the ultimate end use for the ATRP-produced copolymer and, therefore, will vary from use-to-use.
Monomers that may be polymerized by the ATRP process of the present invention include all alpha, beta ethylenically unsaturated monomers that are known to be capable of polymerization by the ATRP process. Any radically polymerizable alkene containing a polar group can serve as a monomer for polymerization. The preferred monomers include those of the formula (II): 
wherein R4 and R5 are independently selected from the group consisting of H, halogen, CN, CF3, straight or branched alkyl of 1 to 20 carbon atoms (preferably from 1 to 6 carbon atoms, more preferably from 1 to 4 carbon atoms), aryl, xcex1,xcex2-unsaturated straight or branched alkenyl or alkynyl of 2 to 10 carbon atoms (preferably from 2 to 6 carbon atoms, more preferably from 2 to 4 carbon atoms), xcex1,xcex2-unsaturated straight or branched alkenyl of 2 to 6 carbon atoms (preferably vinyl) substituted (preferably at the xcex1-position) with a halogen (preferably chlorine), C3-C8 cycloalkyl, heterocyclyl, phenyl which may optionally have from 1-5 substituents on the phenyl ring, C(xe2x95x90Y)R8, C(xe2x95x90Y)NR9 R10, YCR9 R10 R11 and YC(xe2x95x90Y)R11, where Y may be NR11 or O (preferably O), R8 is alkyl of from 1 to 20 carbon atoms, alkoxy of from 1 to 20 carbon atoms, aryloxy or heterocyclyloxy, R9 and R10 are independently H or alkyl of from 1 to 20 carbon atoms, or R9 and R10 may be joined together to form an alkylene group of from 2 to 5 carbon atoms, thus forming a 3- to 6-membered ring, and R11 is H, straight or branched C1-C20, alkyl and aryl; and
R6 is selected from the group consisting of H, halogen (preferably fluorine or chlorine), C1-C6 (preferably C1) alkyl, CN, COOR12 (where R12 is H, an alkali metal, or a C1-C6 alkyl group) or aryl; or
R4 and R6 may be joined to form a group of the formula (CH2)n, (which may be substituted with from 1 to 2nxe2x80x2 halogen atoms or C1-C4 alkyl groups) or C(xe2x95x90O)xe2x80x94Yxe2x80x94C(xe2x95x90O), where nxe2x80x2 is from 2 to 6 (preferably 3 or 4) and Y is as defined above; or
R7 is the same as R4 or R5 or optionally R7 is a CN group; at least two of R4, R5, and R6 are H or halogen.
In the context of the present application, the terms xe2x80x9calkylxe2x80x9d, xe2x80x9calkenylxe2x80x9d and xe2x80x9calkynylxe2x80x9d refer to straight-chain or branched groups.
Furthermore, in the present application, xe2x80x9carylxe2x80x9d refers to phenyl, naphthyl, phenanthryl, phenalenyl, anthracenyl, triphenylenyl, fluoranthenyl, pyrenyl, pentacenyl, chrysenyl, naphthacenyl, hexaphenyl, picenyl and perylenyl (preferably phenyl and naphthyl), in which each hydrogen atom may be replaced with alkyl of from 1 to 20 carbon atoms (preferably from 1 to 6 carbon atoms and, more preferably, methyl), alkyl of from 1 to 20 carbon atoms (preferably from 1 to 6 carbon atoms and, more preferably, methyl) in which each of the hydrogen atoms is independently replaced by a halide (preferably a fluoride or a chloride), alkenyl of from 2 to 20 carbon atoms, alkynyl of from 1 to 20 carbon atoms, alkoxy of from 1 to 6 carbon atoms, alkylthio of from 1 to 6 carbon atoms, C3-C8 cycloalkyl, phenyl, halogen, NH2, C1-C6-alkylamino, C1-C6-dialkylamino, and phenyl which may be substituted with from 1 to 5 halogen atoms and/or C1-C4 alkyl groups. (This definition of xe2x80x9carylxe2x80x9d also applies to the aryl groups in xe2x80x9caryloxyxe2x80x9d and xe2x80x9caralkylxe2x80x9d.) Thus, phenyl may be substituted from 1 to 5 times and naphthyl may be substituted from 1 to 7 times (preferably, any aryl group, if substituted, is substituted from 1 to 3 times) with one of the above substituents. More preferably, xe2x80x9carylxe2x80x9d refers to phenyl, naphthyl, phenyl substituted from 1 to 5 times with fluorine or chlorine, and phenyl substituted from 1 to 3 times with a substituent selected from the group consisting of alkyl of from 1 to 6 carbon atoms, alkoxy of from 1 to 4 carbon atoms and phenyl. Most preferably, xe2x80x9carylxe2x80x9d refers to phenyl and tolyl.
In the context of the present invention, xe2x80x9cheterocyclylxe2x80x9d refers to pyridyl, furyl, pyrrolyl, thienyl, imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl, pyridazinyl, pyranyl, indolyl, isoindolyl, indazolyl, benzofuryl, isobenzofuryl, benzothienyl, isobenzothienyl, chromenyl, xanthenyl, purinyl, pteridinyl, quinolyl, isoquinolyl, phthalazinyl, quinazolinyl, quinoxalinyl, naphthyridinyl, phenoxathiinyl, carbazolyl, cinnolinyl, phenanthridinyl, acridinyl, 1,10-phenanthrolinyl, phenazinyl, phenoxazinyl, phenothiazinyl, oxazolyl, thiazolyl, isoxazolyl, isothiazolyl, and hydrogenated forms thereof known to those in the art. Preferred heterocyclyl groups include pyridyl, furyl, pyrrolyl, thienyl, imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl, pyridazinyl, pyranyl and indolyl, the most preferred heterocyclyl group being pyridyl. Accordingly, suitable vinyl heterocyclyls to be used as a monomer in the present invention include 2-vinyl pyridine, 4-vinyl pyridine, 2-vinyl pyrrole, 3-vinyl pyrrole, 2-vinyl oxazole, 4-vinyl oxazole, 5-vinyl oxazole, 2-vinyl thiazole, 4-vinyl thiazole, 5-vinyl thiazole, 2-vinyl imidazole, 4-vinyl imidazole, 3-vinyl pyrazole, 4-vinyl pyrazole, 3-vinyl pyridazine, 4-vinyl pyridazine, 3-vinyl isoxazole, 3-vinyl isothiazoles, 2-vinyl pyrimidine, 4-vinyl pyrimidine, 5-vinyl pyrimidine, and any vinyl pyrazine, the most preferred being 2-vinyl pyridine. The vinyl heterocyclyls mentioned above may bear one or more (preferably 1 or 2) C1-C6 alkyl or alkoxy groups, cyano groups, ester groups or halogen atoms, either on the vinyl group or the heterocyclyl group, but preferably on the heterocyclyl group. Further, those vinyl heterocyclyls which, when unsubstituted, contain an Nxe2x80x94H group may be protected at that position with a conventional blocking or protecting group, such as a C1-C6 alkyl group, a tris-C1-C6 alkylsilyl group, an acyl group of the formula R13 CO (where R13 is alkyl of from 1 to 20 carbon atoms, in which each of the hydrogen atoms may be independently replaced by halide, preferably fluoride or chloride), alkenyl of from 2 to 20 carbon atoms (preferably vinyl), alkynyl of from 2 to 10 carbon atoms (preferably acetylenyl), phenyl which may be substituted with from 1 to 5 halogen atoms or alkyl groups of from 1 to 4 carbon atoms, or aralkyl (aryl-substituted alkyl, in which the aryl group is phenyl or substituted phenyl and the alkyl group is from 1 to 6 carbon atoms), etc. (This definition of xe2x80x9cheterocyclylxe2x80x9d also applies to the heterocyclyl groups in xe2x80x9cheterocyclyloxyxe2x80x9d and xe2x80x9cheterocyclic ringxe2x80x9d.)
More specifically, preferred monomers include (but are not limited to) styrene, p-chloromethylstyrene, vinyl chloroacetate, acrylate and methacrylate esters of C1-C20 alcohols, isobutene, 2-(2-bromopropionoxy) ethyl acrylate, acrylonitrile, and methacrylonitrile.
The monomer containing at least one polar group may be present in an amount of 5 to 100 wt % by weight based on the total amount of monomers. A preferred amount of the monomer containing at least one polar group is 10 to 100 wt %; the most preferred amount is 20 to 100 wt % based on the total amount of monomers. This is particularly important in the case of acrylonitrile because an amount of at least 20 wt % assures solvent resistance properties of the resulting polymer A.
Examples of suitable monomers may each be independently selected from vinyl monomers, allylic monomers, olefins, (meth)acrylic acid, (meth)acrylates, (meth)acrylamide, N- and N,N-disubstituted (meth)acrylamides, vinyl aromatic monomers, vinyl halides, vinyl esters of carboxylic acids and mixtures thereof. More specific examples of suitable monomers include, without limitation, C1-C20 alkyl (meth)acrylates (including linear or branched alkyls and cycloalkyls) which include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate and isocane (meth)acrylate; (meth)acrylate esters of C1-C20 alcohols; oxirane functional (meth)acrylates which include, but are not limited to, glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate, and 2-(3,4-epoxycyclohexyl) ethyl(meth)acrylate; hydroxy alkyl (meth)acrylates having from 2 to 4 carbon atoms in the alkyl group which include, but are not limited to, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and hydroxybutyl (meth)acrylate. The residues may each independently be residues of monomers having more than one (meth)acryloyl group, such as (meth)acrylic anhydride, diethyleneglycol bis(meth)acrylate, 4,4xe2x80x2-isopropylidenediphenol bis(meth)acrylate (Bisphenol A di(meth)acrylate), alkoxylated 4,4xe2x80x2-isopropylidenediphenol bis(meth)acrylate, trimethylolpropane tris(meth)acrylate and alkoxylated trimethylolpropane tris(meth)acrylate.
Specific examples of vinyl aromatic monomers that may be used to prepare the polymer include, but are not limited to, styrene, p-chloromethyl styrene, divinyl benzene, vinyl naphthalene and divinyl naphthalene. Vinyl halides that may be used to prepare the graft copolymer include, but are not limited to, vinyl chloride and vinylidene fluoride. Vinyl esters of carboxylic acids that may be used to prepare the graft copolymer include, but are not limited to, vinyl acetate, vinyl butyrate, vinyl 3,4-dimethoxybenzoate and vinyl benzoate.
As used herein and in the claims, by the term xe2x80x9callylic monomer(s)xe2x80x9d it is meant monomers containing substituted and/or unsubstituted allylic functionality, i.e., one or more radicals represented by the following general formula III,
H2Cxe2x95x90C(R1)xe2x80x94CH2xe2x80x94xe2x80x83xe2x80x83(III) 
wherein R1 is hydrogen, halogen or a C1 to C4 alkyl group. Most commonly, R1 is hydrogen or methyl and consequently general formula III represents the unsubstituted (meth)allyl radical. Examples of allylic monomers may each independently be residues that include, but are not limited to, (meth)allyl ethers, such as methyl (meth)allyl ether and (meth)allyl glycidyl ether; allyl esters of carboxylic acids, such as (meth)allyl acetate, (meth)allyl butyrate, (meth)allyl 3,4-dimethoxybenzoate and (meth)allyl benzoate.
Other ethylenically unsaturated radically polymerizable monomers that may be used to prepare the copolymer include, but are not limited to, cyclic anhydrides, e.g., maleic anhydride, 1-cyclopentene-1,2-dicarboxylic anhydride and itaconic anhydride; esters of acids that are unsaturated but do not have xcex1,xcex2-ethylenic unsaturation, e.g., methyl ester of undecylenic acid; diesters of ethylenically unsaturated dibasic acids, e.g., di(C1-C4 alkyl)ethyl maleates; maleimide and N-substituted maleimides.
In an embodiment of the present invention, the monomer includes a hydrophobic residue of a monomer selected from oxirane functional monomer reacted with a carboxylic acid selected from the group consisting of aromatic carboxylic acids, polycyclic aromatic carboxylic acids, aliphatic carboxylic acids having from 6 to 20 carbon atoms and mixtures thereof; C6-C20 alkyl (meth)acrylates, e.g., including those as previously recited herein; aromatic (meth)acrylates, e.g., phenyl (meth)acrylate, p-nitrophenyl (meth)acrylate and benzyl (meth)acrylate; polycyclicaromatic (meth)acrylates, e.g., 2-naphthyl (meth)acrylate; vinyl esters of carboxylic acids, e.g., hexanoic acid vinyl ester and decanoic acid vinyl ester; N,N-di(C1-C8 alkyl) (meth)acrylamides; maleimide; N-(C1-C20 alkyl) maleimides; N-(C3-C8 cycloalkyl) maleimides; N-(aryl) maleimides; and mixtures thereof. Examples of N-substituted maleimides include, but are not limited to, N-(C1-C20 linear or branched alkyl) maleimides, e.g., N-methyl maleimide, N-tertiary-butyl maleimide, N-octyl maleimide and N-icosane maleimide; N-(C3-C8 cycloalkyl) maleimides, e.g., N-cyclohexyl maleimide; and N-(aryl) maleimides, e.g., N-phenyl maleimide, N-(C1-C9 linear or branched alkyl substituted phenyl) maleimide, N-benzyl maleimide and N-(C1-C9 linear or branched alkyl substituted benzyl) maleimide.
The oxirane functional monomer or its residue that is reacted with a carboxylic acid, may be selected from, for example, glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate, 2-(3,4-epoxycyclohexyl) ethyl(meth)acrylate, allyl glycidyl ether and mixtures thereof. Examples of carboxylic acids that may be reacted with the oxirane functional monomer or its residue include, but are not limited to, para-nitrobenzoic acid, hexanoic acid, 2-ethyl hexanoic acid, decanoic acid, undecanoic acid and mixtures thereof.
Other useful monomers include vinyl chloroacetate, isobutene, 2-(2-bromopropionoxy) ethyl acrylate and (meth)acrylonitrile.
In the ATRP preparation of the copolymer, the amounts and relative proportions of the initiator, the transition metal compound and the ligand are those for which ATRP is most effectively performed. The amount of initiator used can vary widely and is typically present in the reaction medium in a concentration of from 10xe2x88x924 moles/liter (M) to 3M, for example, from 10xe2x88x923M to 10xe2x88x921M. As the molecular weight of the copolymer product can be directly related to the relative concentrations of initiator and monomer(s), the molar ratio of initiator to monomer is an important factor in copolymer preparation. The molar ratio of initiator to monomer is typically within the range of 10xe2x88x924:1 to 0.5:1, for example, 10xe2x88x923:1 to 5xc3x9710xe2x88x922:1.
In preparing the copolymer by ATRP methods, the molar ratio of transition metal compound to initiator is typically in the range of 10xe2x88x924:1 to 10:1, for example, 0.1:1 to 5:1. The molar ratio of ligand to transition metal compound is typically within the range of 0.1:1 to 100:1, for example, 0.2:1 to 10:1.
The copolymer may be prepared in the absence of solvent, i.e., by means of a bulk polymerization process. Generally, the copolymer is prepared in the presence of a solvent, typically water and/or an organic solvent. Classes of useful organic solvents include, but are not limited to, esters of carboxylic acids, ethers, cyclic ethers, C5-C10 alkanes, C5-C8 cycloalkanes, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, amides, nitriles, sulfoxides, sulfones and mixtures thereof. Supercritical solvents, such as CO2, C1-C4 alkanes and fluorocarbons, may also be employed. A preferred class of solvents are the aromatic hydrocarbon solvents, particularly preferred examples of which are xylene, toluene and mixed aromatic solvents such as those commercially available from Exxon Chemical America under the trademark SOLVESSO. Additional solvents are described in further detail in U.S. Pat. No. 5,807,937 at column 21, line 44 through column 22, line 54.
The ATRP preparation of the copolymer is typically conducted at a reaction temperature within the range of 25xc2x0 C. to 140xc2x0 C., e.g., from 50xc2x0 C. to 100xc2x0 C., and a pressure within the range of 1 to 100 atmospheres, usually at ambient pressure. The ATRP is typically completed in less than 24 hours, e.g., between 1 and 8 hours.
The ATRP transition metal catalyst and its associated ligand are typically separated or removed from the copolymer product prior to its use, for instance, as an adhesion-promoting additive. Removal of the ATRP catalyst may be achieved using known methods, including, for example, adding a catalyst binding agent to the mixture of the copolymer, solvent and catalyst, followed by filtering. Examples of suitable catalyst binding agents include, for example, alumina, silica, clay or a combination thereof. A mixture of the copolymer, solvent and ATRP catalyst may be passed through a bed of catalyst binding agents. Alternatively, the ATRP catalyst may be oxidized in situ, the oxidized residue of the catalyst being retained in the polymer.
The copolymer can be a block copolymer having one or more segments. In a two-segment copolymer, the copolymer may have the general formula IV:
xcfx86-(Ap-Bs-X)txe2x80x83xe2x80x83(IV) 
where each of A and B in general formula IV may represent one or more types of monomer residues, while p and s represent the average total number of A and B residues occurring per block or segment of A residues (A-block or A-segment) and B residues (B-block or B-segment), respectively, and t refers to the number of initiator sites present on the initiator, xcfx86. When containing more than one type or species of monomer residue, the A- and B-blocks may each have at least one of random block, e.g., di-block and tri-block, alternating and gradient architectures. Gradient architecture refers to a sequence of different monomer residues that change gradually in a systematic and predictable manner along the polymer backbone. For purposes of illustration, an A-block containing 6 residues of methyl methacrylate (MMA) and 6 residues of ethyl methacrylate (EMA), for which p is 12, may have di-block, tetra-block, alternating and gradient architectures as represented in general formulas V, VI, VII and VIII.
Di-Block Architecture 
-(MMA-MMA-MMA-MMA-MMA-MMA-EMA-EMA-EMA-EMA-EMA-EMA)-xe2x80x83xe2x80x83V 
Tetra-Block Architecture 
-(MMA-MMA-MMA-EMA-EMA-EMA-MMA-MMA-MMA-EMA-EMA-EMA)-xe2x80x83xe2x80x83VI 
xe2x80x83Alternating Architecture
-(MMA-EMA-MMA-EMA-MMA-EMA-MMA-EMA-MMA-EMA-MMA-EMA)-xe2x80x83xe2x80x83VII 
Gradient Architecture 
-(MMA-MMA-MMA-EMA-MMA-MMA-EMA-EMA-MMA-EMA-EMA-EMA)-xe2x80x83xe2x80x83VIII 
The B-block may be described in a manner similar to that of the A-block.
The order in which monomer residues occur along the polymer backbone of the copolymer is typically determined by the order in which the corresponding monomers are fed into the vessel in which the controlled radical polymerization is conducted. For example, in reference to general formula IV, the monomers that are incorporated as residues in the A-block of the copolymer are generally fed into the reaction vessel prior to those monomers that are incorporated as residues in the B-block.
During formation of the A- and B-blocks, if more than one monomer is fed into the reaction vessel at a time, the relative reactivities of the monomers typically determine the order in which they are incorporated into the living polymer chain. Gradient sequences of monomer residues within the A- and B-blocks can be prepared by controlled radical polymerization, and in particular by ATRP methods by (a) varying the ratio of monomers fed to the reaction medium during the course of the polymerization, (b) using a monomer feed containing monomers having different rates of polymerization, or (c) a combination of (a) and (b). Copolymers containing gradient architecture are described in further detail in U.S. Pat. No. 5,807,937 at column 29, line 29 through column 31, line 35.
Subscripts p and s represent average numbers of residues occurring in the respective A- and B-blocks. Typically, subscript s has a value of at least 1, and preferably at least 5 for general formula IV. Also, subscript s has a value of typically less than 300, preferably less than 100, and more preferably less than 50, e.g., 20 or less, for general formula IV. The value of subscript s may range between any combination of these values, inclusive of the recited values, e.g., s may be a number from 1 to 100. Subscript p may be 0, or may have a value of at least 1, and preferably at least 5. Subscript p also typically has a value of less than 300, preferably less than 100, and more preferably less than 50, e.g., 20 or less. The value of subscript p may range between any combination of these values, inclusive of the recited values, e.g., p may be a number from 0 to 50.
The copolymer can have any suitable number average molecular weight (Mn). Suitable number average molecular weights can be from 5,000 to 50,000, preferably from 12,000 to 40,000 most preferably from 17,000 to 30,000, as determined by gel permeation chromatography using polystyrene standards. The polydispersity index, i.e., weight average molecular weight (Mw) divided by Mn, of the graft portion of the copolymer is typically less than 2.0, e.g., less than 1.8 or less than 1.5.
Symbol xcfx86 of general formula I is, or is derived from, the residue of the initiator used in the preparation of the copolymer by controlled radical polymerization, and is free of the radically transferable group (dormant halide) of the initiator.
The symbol xcfx86 may also represent a derivative of the residue of the initiator. For example, if the initiators have oxyranyl group-containing moieties grafted thereto, the oxyranyl groups may be reacted either prior to or after the completion of the controlled radical polymerization with a carboxylic acid group-containing material. Classes of carboxylic acid group-containing materials with which oxyranyl functional initiators or their residues may be reacted include, for example, aromatic carboxylic acids, polycyclic aromatic carboxylic acids, aliphatic carboxylic acids having from 6 to 20 carbon atoms, and mixtures thereof. Specific examples of carboxylic acid group-containing materials with which oxyranyl functional initiators or their residues may be reacted may include, but are not limited to, para-nitrobenzoic acid, hexanoic acid, 2-ethyl hexanoic acid, decanoic acid, undecanoic acid and mixtures thereof.
In another embodiment of the present invention, a segment of the copolymer, i.e., the xe2x80x94(A)pxe2x80x94 segment in general formula IV can serve as a linking segment between the hydrophobic residue of the initiator, i.e., xcfx86- in general formula IV, and a hydrophilic segment, i.e., the xe2x80x94(B)sxe2x80x94 segment in general formula IV. In reference to general formula IV, A may be a residue of C1-C4 alkyl (meth)acrylates. Examples of C1-C4 alkyl (meth)acrylates of which A may be a residue include, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate and mixtures thereof.
Hydrophilic segments, i.e., xe2x80x94(B)sxe2x80x94 in reference to general formula IV, may have nonionic moieties, ionic moieties and combinations thereof. The segment can comprise residues of a monomer selected from, for example, poly(alkylene glycol) (meth)acrylates; C1-C4 alkoxy poly(alkylene glycol) (meth)acrylates; hydroxyalkyl (meth)acrylates having from 2 to 4 carbon atoms in the alkyl group; N-(hydroxy C1-C4 alkyl) (meth)acrylamides (e.g., N-hydroxymethyl (meth)acrylamide and N-(2-hydroxyethyl) (meth)acrylamide); N,N-di-(hydroxy C1-C4 alkyl) (meth)acrylamides (e.g., N,N-di(2-hydroxyethyl) (meth)acrylamide); carboxylic acid functional monomers; salts of carboxylic acid functional monomers; amine functional monomers; salts of amine functional monomers; and mixtures thereof.
Hydrophilic segments including poly(alkylene glycol) (meth)acrylates and C1-C4 alkoxy poly(alkylene glycol) (meth)acrylates may be prepared by known methods. For example, (meth)acrylic acid or hydroxyalkyl (meth)acrylate, e.g., 2-hydroxyethyl (meth)acrylate, may be reacted with one or more alkylene oxides, e.g., ethylene oxide, propylene oxide and butylene oxide. Alternatively, an alkyl (meth)acrylate may be transesterified with a C1-C4 alkoxy poly(alkylene glycol), e.g., methoxy poly(ethylene glycol). Examples of preferred poly(alkylene glycol) (meth)acrylates and C1-C4 alkoxy poly(alkylene glycol) (meth)acrylates include, poly(ethylene glycol) (meth)acrylate and methoxy poly(ethylene glycol) (meth)acrylate, the poly(ethylene glycol) moiety of each having a molecular weight of from 100 to 800. An example of a commercially available C1-C4 alkoxy poly(alkylene glycol) (meth)acrylate is methoxy poly(ethylene glycol) 550 methacrylate monomer from Sartomer Company, Inc.
A segment of the copolymer may include carboxylic acid functional monomers which include, but are not limited to, (meth)acrylic acid, maleic acid, fumaric acid and undecylenic acid. For instance, in general formula IV, B may initially be a residue of a precursor of a carboxylic acid functional monomer that is converted to a carboxylic acid residue after completion of the controlled radical polymerization, e.g., maleic anhydride, di(C1-C4 alkyl) maleates and C1-C4 alkyl (meth)acrylates. For example, residues of maleic anhydride can be converted to diacid residues, ester/acid residues or amide/acid residues by art-recognized reactions with water, alcohols or primary amines, respectively. Residues of C1-C4 alkyl (meth)acrylates, such as t-butyl methacrylate, can be converted to (meth)acrylic acid residues by art-recognized ester hydrolyzation methods, which typically involve the concurrent removal of an alcohol, such as t-butanol by vacuum distillation. Salts of carboxylic acid functional monomers include, for example, salts of (meth)acrylic acid and primary, secondary or tertiary amines, such as, butyl amine, dimethyl amine and triethyl amine.
The copolymer may contain a segment that contains amine functional monomers which include, for example, amino(C2-C4 alkyl) (meth)acrylates, e.g., 2-aminoethyl (meth)acrylate, 3-aminopropyl (meth)acrylate and 4-aminobutyl (meth)acrylate; N-(C1-C4 alkyl)amino(C2-C4 alkyl) (meth)acrylates, e.g., N-methyl-2-aminoethyl (meth)acrylate; and N,N-di(C1-C4 alkyl)amino(C2-C4 alkyl) (meth)acrylates, e.g., N,N-dimethyl-2-aminoethyl (meth)acrylate. A segment may also comprise residues of salts of amine functional monomers, e.g., salts of those amine functional monomers as recited previously herein. Salts of the amine functional monomer residues may be formed by mixing a carboxylic acid, e.g., lactic acid, with the copolymer after completion of controlled radical polymerization.
In one embodiment of the copolymer, a segment contains carboxylic acid functional monomers selected from (meth)acrylic acid, maleic anhydride, maleic acid, di(C1-C4 alkyl) maleates, and mixtures thereof. In a still further embodiment of the present invention, amine functional monomers are selected from amino(C2-C4 alkyl) (meth)acrylates, N-(C1-C4 alkyl)amino(C2-C4 alkyl) (meth)acrylates, N,N-di(C1-C4 alkyl)amino(C2-C4 alkyl) (meth)acrylates and mixtures thereof.
A segment of the copolymer may also contain cationic moieties selected from ammonium, sulphonium and phosphonium. Ammonium, sulphonium and phosphonium moieties may be introduced into the graft copolymer by means known to the skilled artisan. For example, when a segment contains N,N-dimethyl-2-aminoethyl (meth)acrylate monomers, the N,N-dimethylamino moieties may be converted to ammonium moieties by mixing an acid, e.g., lactic acid, with the graft copolymer.
When a segment of the copolymer contains residues of oxirane functional monomers, such as glycidyl (meth)acrylate, the oxirane groups may be used to introduce sulphonium or phosphonium moieties into the copolymer. Sulphonium moieties may be introduced into the copolymer by reaction of the oxirane groups with thiodiethanol in the presence of an acid, such as lactic acid. Reaction of the oxirane groups with a phosphine, e.g., triphenyl phosphine or tributyl phosphine, in the presence of an acid, such as lactic acid, results in the introduction of phosphonium moieties into the copolymer.
Other reactive groups, such as carbamate groups, can be incorporated into the copolymer. Carbamate groups, may be introduced by including in the ATRP reaction mixture monomers that include carbamate groups and/or by post-reacting the copolymer to add a carbamate group. For instance, carbamate functional groups can be incorporated into the copolymer by reacting a hydroxyl functional acrylic moiety with a low molecular weight alkyl carbamate such as methyl carbamate. Hydroxyl functional acrylic moieties also can be reacted with isocyanic acid to provide pendant carbamate groups. Likewise, hydroxyl functional copolymers can be reacted with urea to provide pendant carbamate groups.
In a preferred embodiment of the present invention, the radically transferable group is a halide group. Dormant halogens can be removed from the terminus of the graft copolymer by any manner known in the art, such as by HX abstraction. Typically the dormant halogen is removed by means of a mild dehalogenation reaction, that typically is performed as a post-reaction after the graft copolymer has been formed, and in the presence of at least an ATRP catalyst. Preferably, the dehalogenation is performed in the presence of both an ATRP catalyst and its associated ligand.
As discussed above, the ATRP process can be conducted with a sequence of monomers to produce a defined copolymer. Thus, the choice of monomers and the sequence of their reaction with dormant halide groups of the initiator and/or propagating chain will influence the final structure of the copolymer. The choice of macroinitiator also will dictate the physical structure of the copolymer. For instance, initiation with certain dormant halides will be more favorable than others. The degree of branching of the macroinitiator also will affect the final structure of the copolymer. Since the dormant halide groups of the macroinitiator are pendant, grafted linear portions of the polyolefin backbone will have a comb-like structure. Macroinitiators with branched structures will yield a more complex, branched copolymer with both comb-like sections, corresponding to relatively linear portions of the backbone, and star-like sections that are the result of grafting onto a tertiary carbon at a branch point between linear portions of the polyolefin backbone. The average weight of the macroinitiator also will dictate the complexity of the resultant copolymer. Lastly, the number of dormant halides on the polyolefin backbone, i.e., the weight percent of active halide groups in the initiator, will effect the structure of the copolymer.
The copolymer prepared according to the methods of the present invention is a copolymer having a polyolefinic backbone and one or more polymer blocks prepared according to the above-described process.
Thus, the copolymer of the present invention includes a polyolefin backbone with pendant halide groups and pendant polymeric blocks of radically polymerizable alkenes containing a polar group that are attached to tertiary carbons of the backbone. The blocks may be of the same monomer, but preferably are of two or more different monomers. The blocks may be homopolymeric or copolymeric. The blocks typically are attached sequentially to the polyolefin backbone, as in general structure (IX):
POxe2x80x94(Axe2x80x94Bxe2x80x94X)nxe2x80x83xe2x80x83(IX) 
Where PO is the backbone, n is an integer greater than 0, A is a first block of monomers, B is a second block of monomers and X is a dormant halide. The monomer content of each of block A and B differ. By xe2x80x9cmonomer contentxe2x80x9d it is meant both the type of monomer, i.e., GMA vs. MMA, and the relative ratio of the monomers, by weight, in each block. It should be noted that in certain circumstances, even though blocks of A are attached directly to the backbone, blocks of B may also be attached directly to the backbone. This can result from the incomplete use of dormant halides on the backbone. In such a case, at least three types of grafts exist, according to the following: xe2x80x94Axe2x80x94X. xe2x80x94Axe2x80x94Bxe2x80x94X and xe2x80x94Bxe2x80x94X, each of which may exist on the same or different backbone. The relative amount of each of these grafts will depend on the reaction conditions and structure of the initiator, and is dependent upon the relative initiation and propagation contents for the respective dormant halides and monomers chosen under the specific reaction conditions.
In one embodiment of the present invention, the copolymer is used as an additive for a film-forming composition. The additive promotes adhesion of the film-forming composition to a polyolefinic substrate, thereby preventing delamination of the film-forming composition from the substrate.
The copolymer typically is present in the film-forming composition in an amount of at least 1.5% by weight, preferably at least 3% by weight, and more preferably at least 5% by weight, based on the total weight of the resin solids other than the copolymer in the film-forming composition. The copolymer is also typically present in the film-forming composition in an amount of less than 20% by weight, preferably less than 5% by weight, and more preferably less than 3% by weight, based on the total weight of the resin solids in the film-forming composition. The amount of copolymer present in the film-forming composition of the present invention may range between any combination of these values, inclusive of the recited values.
Nevertheless, depending upon the structure of the copolymer, and the active groups present thereon, the copolymer can serve as a primary film-forming resin in a coating. In this particular embodiment, the graft copolymer is typically present in the film forming composition in an amount of about 50% to 100% by weight, preferably 45% to 100% by weight.
A crosslinking agent typically is present in the film-forming composition. Generally, the crosslinking agent is an aminoplast or an isocyanate. An aminoplast crosslinking agent is commonly a partially or fully alkylated aminoplast crosslinking agent. The aminoplast crosslinking agent can have a plurality of functional groups, for example, alkylated methylol groups, that are reactive with the pendant carbamate groups present in the acrylic, polyester, polyurethane or polyether polymer.
Aminoplast resins, which include phenoplasts, as curing agents for hydroxyl, carboxylic acid and carbamate functional group-containing materials are well-known in the art. Aminoplast crosslinking agents are obtained from the reaction of formaldehyde with an amine and/or an amide. Melamine, urea, or benzoguanamine condensates are preferred. However, aminoplast condensates prepared from other amines or amides can be used, for example, aldehyde condensates of glycouril, which are useful in formulating powder coatings. Most often, formaldehyde is used as the aldehyde; however, other aldehydes such as acetaldehyde, crotonaldehyde, and benzaldehyde are also suitable.
By the term xe2x80x9cfully alkylatedxe2x80x9d it is meant that the alkylol groups associated with the reaction product of an aldehyde with an amine and/or an amide have been etherified to an extent that the alkoxy groups make up at least 80% by weight of the functional groups.
A preferred aminoplast crosslinking agent is a melamine-formaldehyde condensate that has been fully alkylated, that is, the melamine-formaldehyde condensate contains methylol groups that have been further etherified with an alcohol, preferably one that contains 1 to 6 carbon atoms. Any monohydric alcohol can be employed for this purpose, including methanol, ethanol, n-butanol, isobutanol, and cyclohexanol. Most preferably, a blend of methanol and n-butanol is used. Suitable aminoplast resins are commercially available from Cytec Industries, Inc. under the trademark CYMEL(copyright) and from Solutia, Inc. under the trade name RESIMENE(copyright).
The aminoplast curing agent is typically present in the compositions of the invention in an amount ranging from 2 to 60 wt. %, preferably from 10 to 50 wt. %, and more preferably from 15 to 45 wt. % based on the total weight of resin solids in the composition.
The curing agent may also be a polyisocyanate that optionally can be added as an adjuvant curing agent, along with an aminoplast. As used herein and in the claims, the term xe2x80x9cpolyisocyanatelxe2x80x9d is intended to include blocked (or capped) polyisocyanates as well as unblocked polyisocyanates. The polyisocyanate can be an aliphatic or an aromatic polyisocyanate or a mixture of the two. Diisocyanates may be used, although higher polyisocyanates such as isocyanurates of diisocyanates are preferred. Higher polyisocyanates can also be used in combination with diisocyanates. Isocyanate prepolymers, for example, reaction products of polyisocyanates with polyols, can also be used. Mixtures of polyisocyanate curing agents can be used.
Examples of suitable aliphatic diisocyanates are straight-chain aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate and 1,6-hexamethylene diisocyanate. Also, cycloaliphatic diisocyanates can be employed. Examples include isophorone diisocyanate and 4,4xe2x80x2-methylene-bis(cyclohexyl isocyanate). Examples of suitable aromatic diisocyanates are p-phenylene diisocyanate, diphenylmethane-4,4xe2x80x2-diisocyanate and 2,4- or 2,6-toluene diisocyanate. Other diisocyanates include 1,3-bis(1-isocyanato-1-methylethyl)benzene. Examples of suitable higher polyisocyanates are triphenylmethane-4,4xe2x80x2,4xe2x80x3-triisocyanate, 1,2,4-benzene triisocyanate and polymethylene polyphenyl isocyanate. Other polyisocyanates include biurets and isocyanurates of diisocyanates, including mixtures thereof, such as the isocyanurate of hexamethylene diisocyanate, the biuret of hexamethylene diisocyanate, and the isocyanurate of isophorone diisocyanate. Isocyanate prepolymers, for example, reaction products of polyisocyanates with polyols such as neopentyl glycol and trimethylol propane or with polymeric polyols such as polycaprolactone diols and triols (NCO/OH equivalent ratio greater than one), can also be used.
If the polyisocyanate is blocked or capped, any suitable aliphatic, cycloaliphatic, or aromatic alkyl monoalcohol known to those skilled in the art can be used as a capping agent for the polyisocyanate including, for example, lower aliphatic alcohols such as methanol, ethanol, and n-butanol; cycloaliphatic alcohols such as cyclohexanol; aromatic-alkyl alcohols such as phenyl carbinol and methylphenyl carbinol; and phenolic compounds such as phenol itself and substituted phenols wherein the substituents do not affect coating operations, such as cresol and nitrophenol.
Glycol ethers may also be used as capping agents. Suitable glycol ethers include ethylene glycol butyl ether, diethylene glycol butyl ether, ethylene glycol methyl ether and propylene glycol methyl ether. Other suitable capping agents include oximes, pyrazoles and lactams. One particular example is isophorone diisocyanate capped with methyl ethyl ketoxime.
When used, the polyisocyanate curing agent is present in an amount ranging from 1 to 40 wt. %, preferably from 1 to 20 wt. %, more preferably 1 to 10 wt. % based on the total weight of resin solids in the film-forming composition.
Examples of other blocked polyisocyanates include triazine compounds having the formula C3N3(NHCOXR)3, wherein X is nitrogen, oxygen, sulfur, phosphorus, or carbon, and R is an alkyl group having one to twelve, preferably one to four, carbon atoms, or mixtures of such alkyl groups. X is preferably oxygen or carbon, more preferably oxygen. R preferably has one to eight carbon atoms, for example, methyl, ethyl, n-propyl, isopropyl, butyl, n-octyl and 2-ethylhexyl. R is preferably a mixture of methyl and butyl groups. Such compounds, and the preparation thereof, are described in detail throughout U.S. Pat. No. 5,084,541, incorporated herein by reference. Examples of triazine compounds are tris carbamoyl triazine or 1,2,5 triazine-2,4,6 tris-carbamic acid esters. When used, the triazine curing agent is present in the film-forming composition in an amount ranging from 1 to 40 wt. %, preferably from 1 to 20 wt. %, more preferably 1 to 10 wt. % based on the total weight of resin solids in the film-forming composition.
Optionally, a diluent can be present in the film-forming composition, that serves to reduce the viscosity of the coating composition. If the coating composition is solvent-borne, the diluent typically comprises an organic solvent. Examples of suitable solvents include alcohols such as ethanol, isopropanol, n-butanol, and the like; esters such as n-butyl acetate, n-hexyl acetate, pentyl propionate, and the like; ethers such as the monoethyl, monobutyl and monohexyl ethers of ethylene glycol and propylene glycol, and the like; ketones such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and the like; aromatic hydrocarbons such as xylene, or toluene, and the like; aliphatic or alicyclic hydrocarbons such as the various petroleum naphthas and cyclohexane; and mixtures thereof.
When present, diluents are typically used at a level of up to about 97% by weight based on the total weight of the film-forming composition.
The film-forming composition can also be used in particulate form, i.e., as a powder coating, in which the acrylic polymer and the oligomer or polymer containing the repeating ester groups are chosen such that they have a glass transition temperature (Tg) greater than 60xc2x0 C. These materials can then be combined with an aldehyde condensate of glycouril, as previously mentioned, to form a powder film-forming composition.
The film-forming composition is typically a thermosetting composition and typically contains catalysts to accelerate the curing reactions. Typically, the catalysts are acidic materials. Sulfonic acids, substituted sulfonic acids and amine neutralized sulfonic acids are preferred, for example, p-toluene sulfonic acid, dodecyl benzene sulfonic acid, dinonylnaphthalene disulfonic acid, and the like. The catalyst is usually present in an amount of from 0.3 to 5.0 percent, preferably from 0.5 to 1.0 percent, the percentages based on the total weight of resin solids in the coating composition.
The film-forming composition can contain other optional ingredients, such as co-reactive resinous materials, plasticizers, anti-oxidants, UV light absorbers, surfactants, flow control agents, anti-settling agents, and the like. When present, these materials are generally used at a level of less than 25%, preferably less than 10% by weight, the percentages based on the total weight of resin solids in the coating composition. The coating composition can also contain pigment.
The film-forming composition containing additive quantities of the copolymer is applied to a polyolefinic substrate directly. However, since the physical characteristics of the copolymer of the present invention can vary broadly, the copolymer may be present in other coating layers or can find use for purposes other than promoting adhesion to a polyolefinic substrate. In that case, the coating can be applied to any of the various substrates to which it adheres. Specific examples of suitable substrates include metals, wood, glass, cloth, plastic, foam, elastomeric substrates, and the like. Typically, the substrate is metal or plastic and, most typically, a polyolefinic plastic. Optionally, the substrate could have been previously coated with an electrocoat primer and/or a primer surfacer and/or a pigmented basecoat and the film-forming composition of the present invention applied as a clear coat over the pigmented base coat to form a color plus clear composite coating.
The compositions can be applied by conventional means including brushing, dipping, flow coating, spraying, and the like. Preferably, they are applied by spraying. The usual spray techniques and equipment for air-spraying or electrostatic spraying can be used.
The copolymers of the present invention find use in many fields, such as in coating compositions, compositions for molding, extruding and other article fabrication processes, healthcare and personal care compositions and in any other application for polymeric compounds.
The present invention is more particularly described in the following examples, which are intended to be illustrative only, since numerous modifications and variations therein will be apparent to those skilled in the art. Unless otherwise specified, all parts and percentages are by weight.